DE4137240A1 - AFP steel used for prodn. of large forged tools - has low sulphur content and uniformly high tensile strength through tempering - Google Patents

Abstract

Age-hardenable ferritic-pearlitic (AFP) steel is used for the prodn. of forged tools, esp. large tools, compsn. of the steel being 0.20-0.60% C, 0.20-0.95% Si, 0.50-1.80% Mn, 0.008-0.20% S, 0.004-0.04% N, 0.01-0.05% Ti and/or 0.05-0.20% V and/or Nb, with balance Fe and impurities from the smelting process. In addn., the steel contains max. 0.70% Cr and/or 0.10% Al. The steels are made into blocks or cylinders by forging or rolling at 900-1200 deg.C. (final temp. 1000 deg.C), subjected to controlled cooling, and then used in the prodn. of tools requiring a uniform tensile strength of 850-1100 N/mm2 over a cross-sectional area. ADVANTAGE - High strength is achieved without tempering, high S content is unnecessary, uniform hardness is achieved and the steel can be polished?

Description

The invention relates to the use of AFP steels, which are precipitation hardenable ferritic-pearlitic steels, for which Manufacture of large format tools in particular. Under the Term "tools" are those for non-cutting shaping, such as Dies, die casting and extrusion tools as well as plastic molds, Press brake tools and the like, including their parts, but also including parts for tools such as mold frames, Tool holder and the like understood.

With "large format" dimensions are up to 1000 x 1000 mm Cross section meant.

A number of requirements are placed on such tools:

• 1. Good machinability for the machining of the tools,
• 2. strengths up to 1100 N / mm ² as evenly as possible over the entire cross-section,
• 3. good polishability and grain etchability, especially for Plastic molds where there is no segregation and line-free embossing surface arrives, as z. B. at the Manufacture of grained plastic films is required.

So far, have been used exclusively for this purpose Quenched and tempered steels are used, i.e. steels after manufacture the tools need to be hardened and tempered in order to to achieve the required strength of remuneration. Examples of this are the standardized steels No. 1.2312 (40 CrMnMoS 8 6) and 1.2311. However, these steels could not meet the requirements fully guarantee the desired scope.  

The following problems occur in particular with large rod cross sections on:

• - The required remuneration strength is not over the entire Cross-section achieved,
• - due to the abrupt cooling from the austenitizing temperature during hardening, stresses occur in the bars due to warping lead to dimensional changes or cracks,
• - By the necessary to improve machinability relatively high sulfur content up to 0.10% Cross-resistance significantly reduced and the polishability and Scarrability impaired
• - When casting large blocks of more than 50 t arise in the Solidification of the steel melt local segregation of the Alloy elements carbon, chromium, sulfur, manganese and Molybdenum, which deforms into segregations in rows extend and because of their arrangement, their from the bottom different composition and structure adverse effects on the homogeneity of the steel, its Have polishability, machinability and grain etchability. The at the stresses occurring during hardening are thereby increased and increase the risk of failure due to stress cracks.

According to the invention, AFP steels are used to achieve the object with the composition specified in the claims suggested. Such steels are already known for Automotive components and drop forged components (DE 37 19 569 C2), for Components that, like gas exchange valves of internal combustion engines, are exposed to elevated temperatures up to 560 ° C (DE 40 17 973 A1 and DE 40 14 072 A1). However, it was not known of these steels whether they have the catalog of claims mentioned at the outset, in particular at large format tools.  

Compared to the previously known tempering steels, the AFP steels proposed according to the invention for use A number of advantages:

• 1. There is no remuneration for achieving the high strengths required; this also means that the abrupt cooling is no longer necessary austenitizing during hardening and accordingly the crack and risk of warping as a result of the abrupt cooling mentioned;
• 2. A high sulfur content is not necessary because the ferritic pearlitic structure already shows good machinability;
• 3. a uniform hardness across the cross section Precipitation hardening during cooling from the Thermoforming heat (BY state) can be achieved;
• 4. Differences in hardness between segregated and segregation-free Areas are eliminated due to the uniform structure or are significantly lower than with tempered steels;
• 5. has the ferritic-pearlitic precipitation hardened structure good polishability and grain etchability.

The production of tools from the invention for this proposed AFP steels are made by forging or rolling the Cast blocks in the temperature range of 1200-900 ° C with a Final deformation temperature of 1000 ° C on rod or Round dimensions. After hot shaping, cooling is controlled (BY state). The tools are then made from the semi-finished product machined shape.

Claims (4)

1. Use of a precipitation hardening ferritic-pearlitic (AFP) steel consisting of
0.20 to 0.60% carbon,
0.20 to 0.95% silicon,
0.50 to 1.80% manganese,
0.008 to 0.20% sulfur,
0.004 to 0.04% nitrogen,
0.01 to 0.05% titanium and / or
0.05 to 0.20% vanadium and / or niobium
Remainder iron and melting-related impurities
as a material for especially large-format tools for non-cutting shaping. 2. Use of a steel of the composition according to claim 1, which additionally up to 0.70% chrome and / or up to 0.10% aluminum contains for the purpose of claim 1. 3. Use of a steel according to claim 1, which consists of
0.42 to 0.47% C,
0.50 to 0.80% Si,
1.30 to 1.60% Mn,
0.035% P,
0.020 to 0.035% S,
0.1 to 0.15% V,
Remainder iron with impurities due to melting
exists for the purpose of claim 1. 4. Use of a steel according to any one of claims 1 to 3, which is deformed by forging or rolling in the temperature range from 1200 to 900 ° C, with a final deformation temperature of 1000 ° C to rod or round dimensions and cooled after hot shaping, for Tools that require a uniform tensile strength of 850 to 1100 N / mm ² across the cross-section.